Telecommunication company Telstra agreed to cooperate with the Australian Securities and Investments Commission on the investigation on its share price increase last week before it sealed a contract on the National Broadband Network.

Concerns have been raised on its insider trading that helped increase the company's share price late last week before the deal was announced on Sunday.

Media reports have stated that at least $200 million worth of shares from Telstra were traded on Friday. It was said to be the busiest day for stock trading in the last two weeks.

Telstra closed its share seven cents higher in contrast to the previous day.

The corporate watchdog said it will keep an eye on the movements of the company closely in relation to the share price after the concern was raised by opposition Treasury spokesperson Joe Hockey.

Under the contract, Telstra will receive $9 billion to transfer customers to the $43 billion NBN and lease its network's facilities, such as pits, pipes, and ducts, to assist in the construction of the new fibre network.

The telco will also receive $2 billion to relieve itself from providing essential telecom services to parts of the country where services are idle.

Shares of Telstra also has peaked to a four-month high last Monday after investors showed their support of the group's $11 billion broadband deal.